The present invention relates to films that contain either molecular composites of lyotropic liquid crystalline polymers and thermoplastic polymers or block copolymers having rigid or semi-rigid blocks and thermoplastic blocks.
Lyotropic liquid crystalline polymers include polymers such as aramids and polybenzazole polymers. Such polymers are difficult to fabricate into useful shaped objects. Therefore, liquid crystalline polymers are sometimes intimately admixed with thermoplastic polymers to form molecular composites. See, e.g., Hwang et al., "Concept and Overview of Rigid Rod Molecular Composites," The Materials Science and Engineering of Rigid-Rod Polymers at 507-09 (Materials Research Society 1989), which is incorporated herein by reference. It is also known to make block copolymers that contain blocks of thermoplastic polymer and blocks of rigid or semi-rigid polymer. See Harris et al., U.S. Pat. No. 5,089,586 (Feb. 18, 1992); Harris et al., U.S. Pat. No. 5,075,392 (Dec. 24, 1991); Hwang et al., U.S. Ser. No. 07/547,650 (filed Jul. 2, 1990) and Hwang et al., U.S. Ser. No. 07/562,781 (filed Aug. 6, 1990), which are incorporated herein by reference.
Molecular composites and block copolymers are typically fabricated into shaped articles by coagulation from a dope solution. For instance, a dope containing a molecular composite or block copolymer dissolved in a solvent acid may be extruded through a slit die or a tubular die to form a dope film. The dope film is contacted with water or a similar coagulating liquid so that a polymer film is formed. It would be desirable to improve the mechanical properties of such polymer films.